The gp41 subunit of the HIV-1 envelope glycoprotein plays a major role in the fusion of viral and target cell membranes, leading to the release of the viral genetic material into the cell and to initiation of infection. The extracellular region of gp41 contains two heptad repeat (HR) regions that consist of hydrophobic sequences with high alpha-helical propensity, located adjacent to the N-terminal fusion peptide and at the C-terminus of the gp41 ectodomain, respectively. Peptides derived from the and C-terminal HR regions of gp41 have potent inhibitory activity on the membrane fusion step of HIV-1 infection. Biophysical and crystallographic studies suggest that in the fusion-active status, both regions interact with each other to form a six-helix bundle, consisting of three N-terminal and three C-terminal helices packed in the reverse direction and representing the fusion-active gp41 core structure. A conserved hydrophobic deep cavity in the coiled coil of gp41 plays an important role in stabilizing the helical-hairpin structure of the gp41 core and in membrane fusion, suggesting an attractive target for development of anti-HIV-1 agents. We hypothesize that low molecular weight organic compounds that dock into the hydrophobic cavity or bind to other sites of the and C-terminal heptad repeat regions of gp41 may interfere with the formation of the six-helix bundle of the gp41 core and block HIV-1-mediated membrane fusion. The specific aims of this project are: 1) to identify lead antiviral compounds targeted to the HIV-1 gp41 core; 2) to determine the specificity of the lead antiviral compounds interacting with constituents of the HIV-1 gp41 core; 3) to optimize the lead antiviral compounds for generating most active anti-HIV-1 agents. The long-term goal is to develop novel anti-HIV-1 drugs for chemotherapy of HIV-1 infection and AIDS.